Conductive resin molded product having insulating skin and method for forming the same

ABSTRACT

To make the surface of a conductive resin molded product nonconductive with the resin by adopting a carbon nano material as a conductive compounding material, and, accordingly, to make it possible to expand the use of the conductive resin molded product and use it as a base material of electronic equipment.  
     The conductive resin molded product is produced out of composite material of nonconductive resin and the carbon nano material. The conductive resin molded product is comprised of an insulating skin  1  of the resin formed by blend control of the carbon nano material and the conductive core  2  coated with the insulating skin  1.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a conductive resin moldedproduct having an insulating skin produced by a composite consistingnonconductive resin and conductive material, and relates to a method forproducing the same.

[0003] 2. Detailed Description of the Prior Art

[0004] According to a conventional method, nonconductive resin isblended with conductive material such as carbon black and carbon fiber,or metal powder and metal fiber and the composite is then molded toproduce a conductive resin molded product. (for example, refer to anon-patent literature 1).

[0005] Moreover, some conductive molded products are produced byinjection-filling a mold with conductive resin in which a conductivecompounding material such as metal fiber or metal powder is blended withnonconductive resin (for example, refer to the patent literature 1).

[0006] Non-patent literature 1: Ebihara, “Handbook of New PolymerMaterials” P.69 to 74, Maruzen Co., Ltd. Sept. 20, 1989

[0007] Patent literature 1: The Japanese Patent Laid-Open No.1993-131445, P.5

[0008] Conventionally, the conductive resin molded product has beenproduced by blending the conductive compounding material with thenonconductive resin to provide the resin with conductivity. However, asdescribed in the non-patent literature 1 and the patent literature 1,most of the conventional conductive resins have adopted carbon black,carbon fiber, metal powder, or metal fiber which has remarkably largeparticles compared with the molecules of the resin as the conductivecompounding material. When such conductive compounding material isblended to the extent that the resin is able to have conductivity, themolded product has conductivity even on its surface; therefore,insulation treatment of the surface is necessary depending on its use.

[0009] Moreover, the shape of the molded product tends to be restrictedsince the properties of the resin such as lightweight, flexibility,moldability, and processability are deteriorated to cause a hindrance inthe production of the molded product by injection molding and to lowermechanical strength and the like. As a result, there is a problem thatadoption of the above-mentioned technique to a product with a complexshape, even in the usage as a magnetic wave shield material (shieldmaterial for magnetic wave?).

SUMMARY OF THE INVENTION

[0010] The present invention is devised in order to solve the problemsof the conventional conductive resin molded product as mentioned above.The purpose of the present invention is to expand the use of theconductive resin molded product and to provide a new conductive resinmolded product having a new insulating skin which is usable as a basematerial for parts of electronic equipments such as laminated connectorsas well as a method for producing the conductive resin molded product.For this purpose, a carbon nano material is adopted as a conductivecompounding material to make the surface of the conductive resin moldedproduct nonconductive from the resin.

[0011] The conductive resin molded product for the above-mentionedpurpose according to the present invention comprises a resin insulatingskin and a conductive core covered with said skin and, is composed of acomposite containing a non-conductive resin and a carbon nano material.The resin insulating skin is obtainable from molding said composite bycontrolling an amount of the carbon nano material to be composited withthe non-conductive resin.

[0012] Moreover, a molding method for producing a conductive resinmolded product according to the present invention comprises steps of;

[0013] plasticizing a composite material containing a non-conductiveresin and a carbon nano material; and

[0014] injection molding thus plasticized material into a mold cavity toproduce the conductive resin molded product comprising a resininsulating skin and a conductive core covered with said skin. In themethod, an amount of the carbon nano material to be composited with thenon-conductive resin is controlled so as to form the resin insulatingskin in contact with a cavity face during said injection molding.

[0015] A ratio of the carbon nano material to be composited with saidnon-conductive resin dose not exceed 15 weight % based on the compositeto form the resin insulating skin in contact with a cavity face duringsaid injection molding.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is an enlarged cross sectional view of a part of aconductive resin molded product having an insulating skin according tothe present invention.

[0017]FIG. 2 is an explanatory illustration of behavior of a compositeconductive material flowing in the cavity up to completion of thefilling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018]FIG. 1 shows an enlarged cross sectional view of a part of aconductive resin plate mentioned as an example of the present invention,and the reference numeral 1 is an insulating resin skin, the referencenumeral 2 a conductive core coated with the insulating skin 1. Theconductive resin plate is obtained by injection molding a compositeconductive material with which a carbon nano material is blended. It isa flat plate with a thickness of 1.5 to 3.0 mm and an upper face area of30 to 40 cm², and consists of the insulating skin 1 with a thickness of0.1 to 0.2 mm and the core 2 having conductivity brought by the carbonnano material inside of it. The surface of the conductive resin platehas an insulation characteristics of 10¹⁰Ωcm or more in electricresistance.

[0019] Even if the above-mentioned conductive resin plate is in thestate insulated by the surface resin, an end of a conductive part breaksthrough the insulating skin 1 and reaches the core 2 when the partsticks into the resin plate, therefore, the part becomes to beelectrically connected with the conductive core 2. Such conductive resinplate can be used as an electromagnetic wave shield material having aninsulating skin as it is, and can also be used as a base material for alaminated connector. The conductive resin plate is also applicable tomany other uses than those.

[0020] Since the conductive core 2 is coated with the insulating skin 1in the use as the electromagnetic wave shield material, it isunnecessary to take into account electric damage caused by contact withother electronic equipment, parts, or the like. Moreover, since thesurface is made by resin, the surface treatment such as mirror finishingof the surface and embellishment is also easily carried out by aconventional treatment method employed for the resin up to now.

[0021] Although an illustration is omitted here, the laminated connectorcan easily be manufactured by adhering a necessary number of stacksheets together into a laminated plate, cutting this at equal intervalsinto plate bodies in which the insulating skin and the conductive coreare alternately placed, and only cutting the plate body to a necessarydimension in the direction orthogonal to the insulating skin. Thus, aconnector constituted of the conductive cores of the number equal to thestacked sheets is formed into the laminated type connector divided bythe insulating skins.

[0022] In a conventional laminated connector made of rubber, after athin film of rubber provided with conductivity is alternately laminatedwith a thin film of insulating rubber and fix them together, the fixedone is then cut to manufacture the rubber-made laminated connector. Onthe other hand, using the conductive resin molded product having theinsulating skin 1 eliminates the alternate lamination of the insulatingskins, and the laminated plate is easily formed by mutual adhesionbetween the insulating skins, therefore, the manufacture is moresimplified than that using rubber, and the laminated type resinconnector which has been regarded as difficult to manufacture can beprovided at a lower cost.

[0023] Moreover, the carbon nano material is ultrafine particulate and,in a blending quantity not exceeding 15 weight %, since it does notdamage the characteristics of resin and injection molding can beperformed under the conditions set according to a resin, specialtechniques are not required for molding and there is little change inthe properties. Therefore, the resin does not lose its characteristicsby the molding, and the conductive resin plate further improved indimensional accuracy can be obtained as the base material for parts.

[0024] In order to produce the above-mentioned conductive resin plate byinjection molding, composite conductive material blended the carbon nanomaterial not exceeding 15 weight % with nonconductive resin is used. Asthe nonconductive resin, thermoplastic resin used as a molding material,for example, polyethylene, polyester, polyamide, polycarbonate, ABSresin, and liquid crystal polymer can be used.

[0025] Moreover, as a carbon nano materials to be blended with thenonconductive resin, nano fiber (having a diameter of 50-200 nm,preferably, 80-150 nm, and aspect ratio of 100 1000), nano carbon tube(having a diameter of 1-50 nm, preferably, 10- 50 nm, and aspect ratioof 100-1000), fullerene (having a diameter of 0.7-1 nm), or the like canbe mentioned. Since they are more ultrafine particulate than the metalpowder and metal fiber which have been blended as the conductivematerial in the composite conductive material, they have goodconformability to the resins, and have a good dispersion efficiency bykneading. As a result, the properties of the resins such as flexibility,moldability, and processability are not lost.

[0026] In the aforementioned case, it is most preferable that suchcomposite conductive material is pelletized beforehand and supplied toan injection molding machine. However, there is no difficulty in themolding even if both of the resin and carbon nano material aresufficiently kneaded by a kneader and then supplied to the injectionmolding machine. Therefore, the composite conductive material may besupplied by either method.

[0027] The molding conditions of the injection molding machine such astemperature of a heating cylinder, cooling temperature of a productmold, screw speed, injection speed and pressure are arbitrarily setaccording to the kind of resin adopted there. After the compositeconductive material supplied from a hopper into the heating cylinderwith a built-in screw is plasticized (melted and kneaded) by ordinaryinjection molding operation, the material is measured and then filled byinjection into the mold by forward stroke of the screw.

[0028] Each illustration in FIG. 2 shows the behaviors of the moltenbody 13 of the composite conductive material flowing in the cavity 12 ofthe mold 11 before completing the filling, and as shown in theillustration (A), the molten body 13 flows at the highest speed in thecenter part, and flows slower as it approaches to a cavity surface 12 a.Moreover, as shown in the illustration (B), the molten body is increasedin viscosity due to cooling of the mold 11 and gets difficult to flow,and the resin is cooled and solidified into the surface layer (theskin).

[0029] From this difference in flow, a velocity gradient, namely, a rateof shear arises between the center part of the molten body 13 and thecontact part with the cavity surface 12 a. Thus, the resin on the cavitysurface 12 a which is getting cooled and solidified is extended in thedirection of the flow because of large shearing stress applied on itfrom the molten body 13 being press-fitted, and at the same time, thecarbon nano material on the skin side is also pulled and aligned in thedirection of the flow, and also becomes to be easily centralized in thecenter of the molten body from the skin 13 a.

[0030] On the other hand, since the core 13 b is little influenced bythe shearing stress and the carbon nano material exhibits anisotropy,conductivity appears. It is difficult to express conductivity by usingfullerene, but an effect is obtained by using another carbon nanomaterial together. This phenomenon is conditional on a blending quantityof a carbon nano material; the blending quantity is preferred to be 5-15weight %. In the case of a blending quantity exceeding 15 weight %,conductivity appears also on the skin 13 a and this makes it difficultto form the insulating skin 13 a out of the resin. After havingcompleted filling the resin, the resin is cooled and solidified into theconductive resin plate comprising the skin 13 a of the resin havingnon-conductivity and the conductive core 13 b coated with the skin 13 aas shown in the illustration. Namely, the insulating skin formed out ofresin and the core coated with the insulating skin are formed by thedifference in fluidity between the resin and the carbon nano materialflowing in the cavity and shearing stress on the cavity surface obtainedby controlling a blending quantity of a carbon nano material.

[0031] Example of the Embodiment Conductive resin molded product Formand dimensions; Flat plate (rectangular shape), Plate thickness: 2.0 mmPlane area of its upper face: 36 cm² Resin; Polypropylene Compoundingingredient; Carbon nano tube, 10 nm diameter, 1 to 10 μm long Blendingquantity; 10 weight % Conductivity (volume Surface: 10¹⁰ Ωcm or more,resistivity); Inside: 10³ Ωcm or less Injection molding machine; PS40(manufactured by NISSEI PLASTIC INDUSTRIAL CO., LTD.) Moldingconditions; Plasticizing temperature 210° C. Injection speed 100 mm/sInjection pressure 100 MPa Mold temperature 30° C.

What is claimed is:
 1. A conductive resin molded product having a resininsulating skin, said product being composed of a composite containing anon-conductive resin and a carbon nano material, and said productcomprising: a resin insulating skin obtainable from molding saidcomposite by controlling an amount of the carbon nano material to becomposited with the non-conductive resin; and a conductive core coveredwith said skin.
 2. A molding method for producing a conductive resinmolded product, said method comprising the steps of: plasticizing acomposite material containing a non-conductive resin and a carbon nanomaterial; and injection molding thus plasticized material into a moldcavity to produce the conductive resin molded product comprising a resininsulating skin and a conductive core covered with said skin, an amountof the carbon nano material to be composited with the non-conductiveresin being controlled so as to form the resin insulating skin incontact with a cavity face during said injection molding.
 3. The moldingmethod according to claim 2, wherein a ratio of a carbon nano materialto be composited with said non-conductive resin dose not exceed 15weight % based on the composite.